The present invention relates to a permanent magnet type linear motor that causes a relative movement between permanent magnets and an armature coil, being able to a highly accurate positioning.
The conventional linear motor has a plurality of permanent magnets arranged in a yoke through a magnetic gap such that magnetic poles adjacent to each other and facing each other have opposite polarities, and an armature coil is provided in the magnetic gap. The relative movement is caused between the permanent magnets and armature coil by supplying a electric current with the armature coil. The above linear motor is classified into the following two types: a moving-coil type in which the permanent magnets are fixed and the armature coil is moved, and a moving-magnet type in which the armature coil is fixed and the permanent magnets are moved.
In the conventional linear motor, as shown in FIG. 10, a position detection means 100 is provided for position control on a movable member 71. The position detection means 100 consists of a read head 72 provided on the movable member 71 and a linear scale 74 provided on a stator 73. For example, the linear scale 74 is constituted such that reflective or opaque graduations are formed in a transparent glass plate at constant intervals, and these graduations are optically read by the read head 72. Related techniques are disclosed in, for instance, Japanese Patent Application Unexamined Publication No. Sho. 61-103653.
In the conventional linear motor, the linear scale 74 is disposed in the end of the stator 73 and the read head 72 is also disposed in the end of the movable member 71 so as to face the linear scale 74. With the position detection means 100 disposed as above, when, for instance, the movable member 71 is inclined during movement, a deviation may occur in the positional relationship between the read head 72 and the linear scale 74, reducing the reading accuracy of the read head 72. In particular, when the stopping accuracy of the movable member 71 must be less than several micrometers, the reduction in reading accuracy becomes a serious problem.
To solve this problem, the movable member 71 could conceivably be made heavier to thereby prevent inclination. However, this would increase the size of the linear motor and also require a larger thrust that would increase power consumption.